The objective of this research project is to elucidate the mechanism(s) which underlies the association between carcinogenesis and cell proliferation. The technical focus of the project is on a method for purification of eukaryotic replication complexes from the nuclei and proliferating rat liver cells. The proposed studies will utilize this method to elucidate the process of eukaryotic DNA replication and to characterize the effects of carcinogens on biologically determined DNA subfractions. Proposed studies will further characterize the constituents of the replication complex. The observation that replication complexes associated with a specific fraction show the greatest increase in synthesis of DNA at the earliest stages of the S phase suggests a possible method for identification and purification of S phase initiation sites. DNA at the replication complex is preferentially alkylated by chemical carcinogens. Further studies will attempt to determine the mechanism responsible for this specificity. By limiting studies to DNA at replication complexes, a comparison of the alkylation of nascent versus parental DNA will be performed with improved specificity. With DNA from replication complexes visualized by electron microscopy, the relationship of carcinogen binding sites to DNA replication forks will be investigated. Since carcinogen treatment can cause post-replication repair with slowed rates of DNA synthesis, the replication complex isolation technique will be evaluated to determine whether it can purify sites of post-replication repair.